GValueArray of gdouble"decay":
the decaying peak power level in dB for each channel
The decaying peak level follows the peak level, but starts dropping if no
new peak is reached after the time given by the “peak-ttl”.
When the decaying peak level drops, it does so at the decay rate as
specified by the “peak-falloff”.

GValueArray of gdouble"rms":
the Root Mean Square (or average power) level in dB for each channel